Polyimide has been utilized in, for example, a resin for electronic components, a heat-resistant resin, and an abrasion-resistant resin, because it is excellent in chemical stability and thermal stability, and has high mechanical strength. However, the polyimide has a problem in difficulty of processing into a membrane or a film. Therefore, tetracarboxylic dianhydride is subjected to polyaddition reaction with a diamine compound in a high boiling point solvent to thereby obtain a solution of polyamic acid (polyimide precursor). The resultant solution is applied onto a substrate, followed by heating at a high temperature of about 400° C. to thereby imidate the polyamic acid. Then, the solvent is removed to thereby produce a polyamide film. However, there has been a limit to generic use of a polyimide precursor and polyimide.
There has been proposed a method for producing polyimide particles by dissolving polyamic acid into a solvent in which polyimide is insoluble, followed by imidating the polyamic acid with an imidating agent in a high-pressure container filled with carbon dioxide at a pressure of 5 MPa to 30 MPa (see PTL 1).
There also has been proposed a method for producing polyimide particles by mixing a good solvent of polyamic acid with a poor solvent of polyamic acid on a substrate to thereby produce a precipitate (see PTL 2).
However, in these proposed methods, there is a problem that a solvent or an impurity adversely remains in the produced polyamide precursor and polyimide.
Therefore, there has been a demand to provide a method for producing a polyimide precursor capable of efficiently producing a high-quality polyimide precursor containing only a small amount of a residual solvent and impurity.